Disease

[RPGR_HUMAN] Primary ciliary dyskinesia;Achromatopsia;Primary ciliary dyskinesia - retinitis pigmentosa;Cone rod dystrophy;Retinitis pigmentosa. Defects in RPGR are the cause of retinitis pigmentosa type 3 (RP3) [MIM:300029]; also known as X-linked retinitis pigmentosa 3 (XLRP-3) or retinitis pigmentosa type 15 (RP15). A X-linked retinal dystrophy belonging to the group of pigmentary retinopathies. RP is characterized by retinal pigment deposits visible on fundus examination and primary loss of rod photoreceptor cells followed by secondary loss of cone photoreceptors. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well. In RP3, affected males have a severe phenotype, and carrier females show a wide spectrum of clinical features ranging from completely asymptomatic to severe retinitis pigmentosa. Heterozygous women can manifest a form of choroidoretinal degeneration which is distinguished from other types by the absence of visual defects in the presence of a brilliant, scintillating, golden-hued, patchy appearance most striking around the macula, called a tapetal-like retinal reflex.[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Defects in RPGR are the cause of retinitis pigmentosa and sinorespiratory infections with or without deafness (RPDSI) [MIM:300455]. A disease characterized by the association primary ciliary dyskinesia features with retinitis pigmentosa. Some patients also manifest deafness.[15][16] Defects in RPGR are the cause of cone-rod dystrophy X-linked type 1 (CORDX1) [MIM:304020]; also known as cone dystrophy 1 (CO1). CORDs are inherited retinal dystrophies belonging to the group of pigmentary retinopathies. CORDs are characterized by retinal pigment deposits visible on fundus examination, predominantly in the macular region, and initial loss of cone photoreceptors followed by rod degeneration. This leads to decreased visual acuity and sensitivity in the central visual field, followed by loss of peripheral vision. Severe loss of vision occurs earlier than in retinitis pigmentosa. In CORDX1 the degree of rod-photoreceptor involvement can be variable, with degeneration increasing as the disease progresses. Affected individuals (essentially all of whom are males) present with decreased visual acuity, myopia, photophobia, abnormal color vision, full peripheral visual fields, decreased photopic electroretinographic responses, and granularity of the macular retinal pigment epithelium. Although penetrance appears to be nearly 100%, there is variable expressivity with respect to age at onset and severity of symptoms.[17] Defects in RPGR are a cause of macular degeneration X-linked atrophic (MDXLA) [MIM:300834]. MDXLA is an ocular disorder characterized by macular atrophy causing progressive loss of visual acuity with minimal peripheral visual impairment. Some patients manifest extensive macular degeneration plus peripheral loss of retinal pigment epithelium and choriocapillaries. Full-field electroretinograms (ERGs) show normal cone and rod responses in some affected males despite advanced macular degeneration.[18]

Function

[RPGR_HUMAN] Could be a guanine-nucleotide releasing factor. Plays a role in ciliogenesis. Probably regulates cilia formation by regulating actin stress filaments and cell contractility. Plays an important role in photoreceptor integrity. May play a critical role in spermatogenesis and in intraflagellar transport processes (By similarity). May be involved in microtubule organization and regulation of transport in primary cilia.[19]

Publication Abstract from PubMed

Defects in primary cilia result in human diseases known as ciliopathies. The retinitis pigmentosa GTPase regulator (RPGR), mutated in the most severe form of the eye disease, is located at the transition zone of the ciliary organelle. The RPGR-interacting partner PDEdelta is involved in trafficking of farnesylated ciliary cargo, but the significance of this interaction is unknown. The crystal structure of the propeller domain of RPGR shows the location of patient mutations and how they perturb the structure. The RPGR.PDEdelta complex structure shows PDEdelta on a highly conserved surface patch of RPGR. Biochemical experiments and structural considerations show that RPGR can bind with high affinity to cargo-loaded PDEdelta and exposes the Arl2/Arl3-binding site on PDEdelta. On the basis of these results, we propose a model where RPGR is acting as a scaffold protein recruiting cargo-loaded PDEdelta and Arl3 to release lipidated cargo into cilia.